Tanning composition comprising lignin sulfonic acid-chromium compound reaction product



United States Patent fif ce 3,63%,3l Patented June 19, 1962 TANNING COMPOSITION COMPRISING LIGNIN SULFONIC ACID-CHROMIUM COlVIPOUND RE- ACTION PRODUCT Robert G. Banner and John H. Pierce, Painesville, Ohio, assignors to Diamond Alkali Company, Cleveland, Ghio, a corporation of Delaware No Drawing. Filed May 27, 1960, Ser. No. 32,142

20 Claims. (Cl. 894.26)

This invention relates to a new and improved composition for the tanning of leather and more particularly relates to a new and improved chromium-containing tanning composition and to the method of making it.

This application is a continuation-in-part of our copending application Serial No. 650,825, filed April 5, 1957, now abandoned.

At the present time, two recognized types of tanning procedures have been accepted and widely-practiced in the leather industry. These are the so-called vegetable tanning wherein the conversion of the hide to leather is accomplished with aqueous tanning solutions, extracted from materials of vegetable origin, such as finely-ground oak or hemlock bark or the like, and the so-called chrome tanning which utilizes various reducible salts of chromium, notably alkali metal bichromates, and especially sodium bichromate, to effect the conversion of the hides to leather.

Each of these tanning techniques has several advantages which has justified its continued use despite other somewhat serious disadvantages, which at the present time, have not been completely overcome. For example, vegetable tanning produces leather and particularly sole leather of an excellent color, having Wear properties and Waterproofness which are generally quite satisfactory. However, vegetable tanning is an extremely slow process and hence, despite the advantage of producing a so-called full leather of good color, the slowness of vegetable tanning has precluded its use in many applications where it otherwise would be highly desirable.

On the other hand, the outstanding advantage of chrome tanning is the speed with which the tanning is effected. Moreover, chrome-tanned leather exhibits good wear and abrasion resistant properties. However, the principal disadvantages of conventionally chrome-tanned leather, especially when used as sole leather, are that it is susceptible to distortion and at times is slippery on wet surfaces.

In an effort to overcome the recognized disadvantages of vegetable and chrome tanning, prior workers in the art have proposed several variations in tanning procedure. For example, it has been suggested that leather first be tanned with a vegetable tanning material and then retanned with a cationic chromium-containing tanning composition, i.e., the conventional type of chrome tanning composition. Advantages of such a procedure are that a higher shrinkage temperature is obtained, together with increased abrasion resistance, especially in sole leather so prepared. However, it has been found that leather thus-produced frequently has a poor color. Moreover, since such a procedure involves additional treatment, inevitably there is an increase in cost involved. In addition, the extremely slow vegetable tanning process, used as a first step, still is encountere Alternatively, prior workers in the art also have proposed first to chrome tan leather and then to use a vegetable tanning composition as a retan. However, this technique has not been found to be the complete answer to the problem either, because a heavy vegetable tan frequently is required to obtain a satisfactory leather color. Inasmuch, as the desired Wear properties of the leather generally decrease with an increase in the amount of vegetable tanning eiiected, this procedure has resulted in a leather, and particularly sole leather, having poor wear characteristics.

Accordingly, it will be appreciated that up to the present time no completely satisfactory tanning technique has been available for the tanning of leather, particularly leather destined for application as sole leather.

It is, therefore, the principal object of the present invention to provide an improved leather, especially sole leather, characterized by a maximum of the desirable properties of vegetable-tanned leather as well as those of chrome-tanned leather, while minimizing the disadvantages of both tanning techniques.

A further object of the present invention is to provide a new and improved tanning composition by use of which this improved leather can be produced.

These and other objects of the present invention will become apparent to those skilled in the art from the description of the invention which follows.

The present invention envisions a predominantly nonionic, chromium-containing tanning composition which will produce a leather characterized by good color, solidity, fullness, workability, and excellent abrasion and water resistance. Such tanning composition is obtained by chemically reacting lignin sulfonic acid with at least suflicient of a hexavalent chromium compound to produce a predominantly non-ionic, chromium-containing material.

in preparing this non-ionic, chromium-containing composition, the amount of hexavalent chromium compound employed must not be less than about 25% by weight of the lignin sulfonic acid, expressed in terms of lignin solids used in preparing the lignin sulfonic acid. Moreover, it has been found that the amount of hexavalent chromium compound employed should not exceed about 50% by weight of the lignin sulfonic acid, again expressed in terms of lignin solids. It will, of course, be understood that the hexavalent chromium compound may be chromic acid or an alkali metal bichromate, the term alkali metal referring to sodium, potassium, lithium, rubidium and cesium. However, because of its low cost and ready availability, the preferred hexavalent chromium compounds are the alkali metal bichronrates, of which sodium bichromate is the most preferred. For this reason, hereinafter particular reference will be made to sodium bichromate as the source of hexavalent chromium.

The expression lignin sulfonic aci as used throughout the specification and claims is intended to refer to lignin sulfonic acid obtained from neutralized sulfite waste liquors. In practice, these liquors, formed as a by-product from the cooking of wood fibers in the paper industry, are generally neutralized with calcium or magnesium salts and the resulting liquors used as such or spray dried to obtain a crude water-soluble lignin sulfonate, generally calcium sulfonates, or as termed herein, lignin solids. One commercially available product of this type is termed Goulac. The water-soluble lignin solids can be dissolved in Water and acidified prior to use in the practice of this invention, or, if desired, may be formed in situ during the preparation of the composition embodying the present invention.

A typical commercially availabe Goulac (lignin solids) has the following analysis:

Percent by Wgt.

The term non-ionic as applied to chromium throughout the specification and claims is intended to refer to chromium, the major part of which has substantially no electrical charge as detectable by ion exchange techniques. Thus, the chromium-containing tanning composition used in the present method comprises chromium in a non-ionic form as a major ingredient, i.e., an amount of at least 50% by weight. Attention is now directed more specifically to the various aspects of the invention, notably the tanning composition, its preparation and use in tanning.

The tanning composition of this invention comprises the chemical reaction product of a major proportion of lignin sulfonic acid, e.g., prepared by the acidification of dissolved lignin solids, with a minor proportion of a hexavalent chromium compound, e.g., an alkali metal bichromate, preferably sodium bichromate, in the amount of at least 25% by weight of the lignin solids, which amount is sufiicient to produce a predominantly non-ionic, chromium-containing reaction product in which the content of non-ionic chromium is at least 50% by Weight. This composition is desirably partially neutralized to an acid pH within the range from about 3.0 to 4.5, 4.0 being preferred.

The proportion of the reactants which are employed is critical, in that the minimum amount of the hexavalent chromium compound, especially sodium bichromate, which is to be used, must be at least 25% by weight of the lignin solids, which amount is sufiicient so that the reducible hexavalent chromium present is converted in the reaction product to a predominantly non-ionic form in the amount of at least 50% by weight. Moreover, the maximum amount of hexavalent chromium compound to be employed is found to be about 50% by weight of the lignin solids inasmuch as when greater amounts are used, the product does not contain a predominant proportion of non-ionic chromium. Additionally, if an amount of sodium bichromate greater than 50% by weight of the lignin solids is used, the reaction mixture gels and becomes virtually impossible to work with.

Preferably, the reaction product is partially neutralized to reduce its otherwise extremely low pl-I to a higher, but still acid pH of about 3.0 to 4.5, as pointed out hereinabove. The reaction product may be used as such, without further treatment, as a solution or may be concentrated or dried. Preferably, the reaction product is spray dried at an elevated temperature.

In practice, the desired amount of water-soluble lignin solids is dissolved in water, with agitation, and the resultant solution is acidified using a mineral acid, such as hydrochloric or sulfuric acid, the latter of which is preferred. The amount of sulfuric acid used is preferably about 35% by weight of the lignin solids. Alternatively to in situ formation of the lignin sulfonic acid, an aque ous solution of lignin sulfonic acid may be employed. In either case, to the resultant lignin sulfonic acid solution with continuous agitation, is added an aqueous solution of a hexavalent chromium compound. Preferably this is an alkali metal bichromate and especially sodium bichromate, typically as a 50% by weight solution. The rate of addition of this solution is such that in combination with the agitation, the formation of lumps or gel particles is avoided. Typically, in a commercial operation, the addition time is at least one hour, 1-2 hours being preferred. This solution is added in the amount of at least 25% by weight as sodium bichromate, of the lignin solids, and not in excess of 50% by weight as sodium bichromate, of the lignin solids. Continuous agitation is elfected until the chemical reaction and dissolution are complete.

The resultant solution, generally having a pH of about 2, may be used as such in those applications wherein extremely acid material is not objectionable. However, it generally is desirable and is preferred, partially to neutralize this solution by addition of alkali, e.g., sodium hydroxide, sodium bicarbonate or other alkaline subhides to be tanned.

stance, to raise the pH to a value of about 3.0 to 4.5, preferably about 4.0. Generally, the sodium hydroxide is added in an amount of about 11% by weight of the lignin solids used.

The partially neutralized solution then may be used as such or, depending upon the application, may be concentrated or dried. An especially advantageous treatment constitutes spray drying of the material at an elevated temperature. Typical spray drying conditions involve adjusting the desiccating chamber of the dried so as to provide an air inlet temperature of about 300 to 500 F., preferably about 400 F., and an air outlet temperature of about 200 to 250 F., preferably 210 to 230 F.

The practice of the present invention in respect to tanning of leather involves subjecting the hides to be tanned, after conventional soaking or washing, fieshing, dehairing, bating and pickling, to an aqueous solution of a predominantly non-ionic, chromium-containing reaction product obtained by chemically reacting lignin sulfonic acid with the hexavalent chromium compound in the amount of at least 25% by weight of the lignin solids in the lignin sulfonic acid, at an elevated temperature for a period of time sufiicient to effect the desired tanning. In many instances, it is advantageous to soak the stock immediately prior to tanning, in an aqueous solution of an alkali metal halide, notably sodium chloride, e.g., in a 1-15 by Weight sodium chloride solution.

In the carrying out of tanning using the composition of this invention, it is desirable to maintain the pH of the tanning solution within the range of about 4.0 to 6.0, 5.0 being the specifically preferred pH. Additionally, tanning is preferably carried out at temperatures above ordinary room temperature, e.g., from about to F. and preferably about 100 F., although it will be appreciated that in some applications higher tanning temperatures, i.e., to about F. may be used, the upper temperature limit generally being dictated by the quality of leather which is required. Conversely, a minimum practicable tanning solution temperature generally is about 85 F. but is, of course, dictated by the time available for tanning.

The time required for tanning depends on a large number of variables, including the type of stock, thickness, prior treatments, and efiect desired, so that a satisfactory shrink temperature can be obtained. It is understood that by shrink temperature is meant the elevated temperature at which shrinkage of the leather in water, or a glycerine-water mixture, first is observed, which temperature is used as a measure of tanning effectiveness, a

shrink temperature of 200 F. or higher indicating a satisfactorily tanned leather. As a general guide, however, it is desirable to subject the hides to the tanning solution of the present invention for a period of at least 1 hour, typically 1-10 hours and preferably about 8 hours at the temperatures indicated hereinabove. In this manner, shrink temperatures of 200 F. or higher are readily obtained.

The concentration of the tanning solutions may also be varied, it generally being desired to use a tanning solution containing about 20-35% solids, 30% solids being especially preferred, based on the weight of the wet hides to be tanned. Moreover, the amount of the tanning solution used is generally about 60l20% by weight of the wet Following this tanning procedure, the thus-tanned hide may, if desired, advantageously be retanned with a vegetable tanning material, a conventional chrome-tanning material or, with the predominantly non-ionic tanning composition of the present invention or a combination of chrome and vegetable retans. Alternatively, the leather may be used without further treatment or, it may, be fat liquored and/ or waterproofed prior to usage with or without any of the aforementioned retannmgs.

In order that those skilled in the art may better understand the method of the present invention and the manner in which it may be practiced, the following specific examples are given. It is to be understood, of course, that the examples are not to be constituted as limiting the invention but are intended merely to be illustrative thereof.

EXAMPIJE 1 One hundred lbs. of Goulac (lignin solids) is dissolved in 250 lbs. (30 gallons) of water and 35 lbs. of 95% by weight sulfuric acid is added thereto and the resulting mass is agitated for 1 hour, during which time 80 fumes are evolved. Twenty-five lbs. of Na Cr O .2H O as a 50% by weight solution is then added slowly with continuous and vigorous agitation to avoid formation of any chromelignin gel lumps. After all the bichromate solution is added, the mass is agitated for 2 hours after which time 55 lbs. of sodium hydroxide is added, as a 25% solution, with continuing vigorous agitation. :The resultant mixture is allowed to stand overnight, after which time another 5.5 lbs. of sodium hydroxide, as a 25% solution, is added with vigorous agitation and sufiicient water is then added to make a total volume of 50 gallons. The pH of the resultant liquid tanning solution is 4.0. Chemical analysis of the liquid tan so prepared is as follows:

This material can be employed either as a liquid or spray dried, advantageously with the desiccating chamber of the dryer adjusted so as to provide an inlet air temperature of about 400 F. and an outlet air temperature of about 210 to 230 3., during the drying operation.

EXAMPLE 2 Stock, consisting of pickled steer hides, is floated in a tanning drum in a sodium chloride solution for a period of 10 minutes, the amount of sodium chloride solution being equal to the weight of the stock. To the thustreated stock is added the liquid tan prepared in Example 1 in the amount of 50% by weight of the stock. Tanning is carried out for 2 hours at 100 F. after which time an additional quantity of the liquid tan in the amount of 50% by weight of the stock is added and tanning is continued for a total of 4 hours. Thereafter, sodium bicarbonate in the amount of 3% by weight of the stock as a 5% aqueous solution is added to the tanning drum so as to raise the pH of the tanning solution to 5.0. Tanning is continued for a total tanning time of 8 hours, after which time a shrink temperature of 200 F. is obtained. The stock is then horsed up overnight and washed with water until a clear efliuent is obtained. The thus-tanned leather may be employed as such or may be subjected to further treatment as indicated in the following examples.

CrzOs, A1203, Basicity, percent percent percent basicity being defined as the percent of total chromium EXAMPLE 4 Stock produced in accordance with Example 2 is retanned with a vegetable tan. 2 to 4% of a fat liquor is added to the vegetable tan after /1 hour of the tanning run. Using this procedure an excellent leather is obtained.

EXAMPLE 5 The leather produced in accordance with Examples 2 and 3 is fat liquored using a 2% solution of Neutrolene 7A (a cationic-non-ionic animal type fat liquor) in an amount equal to the weight of the stock to be fat liquored, at 120 F. Using this procedure, a complete take up of the fat liquor by the stock is efiected. Advantageous fat liquoring can also be effected using a fat liquor comprising raw neats-fcot oil and an emulsifier therefor such as the various cationic emulsifying materials.

Leather treated with the composition of the present invention, if desired, may be rendered even more waterrepellant by further treatment with a water repellant, such as silicone resins, e.g., Dow Corning Silicone 1109 or Quilon (stearato chrome complex in isopropyl alcohol).

EXAMPLE 6 To illustrate the excellent properties of leather obtained by the practice of the present invention, leather tanned in accordance with the procedure set forth in Example 2 is subjected to water absorption tests in which a weighed specimen of leather is immersed in distilled water for periods of 30 minutes and 120 minutes, any gain in weight being calculated as a percentage gain of the conditioned weight of the sample. Additionally, the leather is subjected to an abrasion test using a US. Bureau of Standards abrasion testing machine in which the wear loss in thickness is measured against a standard sole leather and the results reported in the number of cycles necessary to wear away 0.05 inch and 0.10 inch using 1 x 1 inch test pieces with 3M No. 2% garnet paper. In these tests, leather tanned using the chromium tanning compositions prepared in accordance with Example 1 is compared to leather tanned with a composition prepared in the same manner with the exception that the amount of sodium bichromate used is only 20% by Weight of the lignin solids rather than 25 by weight. Additionally, two tests are made using leather tanned with a tanning composition prepared by reacting the lignin sulfonic acid with and sodium bichromate by weight of the lignin solids. The results of these tests are as follows Percent Water Abrasion Cycles Sodium Bichro- Absorptwn Test N o. mate/Liguin Solids Ratio 0. 05 0.10 0.5 2.0

In. In. hour hours 0. 20 2, 167 2, 983 16. l 28. 8 0. 25 2, 883 5, 273 12. 3 24. 1 0. 20 742 29. 6 56. 4 0. 25 1, 067 25. 7 48. 3 0. 20 658 1, 033 10. 3 18. 2 0. 25 1, 858 2, 658 7. 2 12. 0 0. 20 425 700 17. 8 34. 4 0. 25 538 790 13. 7 27. 9 0. 20 1, 062 1, 685 O. 25 1, 700 2, 617 0.20 2, 017 3, 033 21. 6 31. 8 0. 25 2, 592 4, 553 19.3 32. 0 0. 20 942 1, 217 31. 2 52. 8 0. 25 1, 378 1, 708 30. 5 47. O 0. 20 l, 208 1, 825 19. 0 37. 5 0. 25 2, 123 4, 317 14. 0 27. 0 O. 20 3,150 6, 933 8, 5 19. 1 0. 25 4, 883 10, 133 15. 5 28. 3 0. 20 3, 910 8, 225 6. 3 11. 4 0. 25 3, 872 9, 783 5. 5 10. 1 0. 20 1, 013 1, 487 11. 8 20. 8 O. 25 3, 038 3, 642 11. 2 19.8 0. 35 2, 467 5, 167 12. 1 21. 5 0. 40 2, 943 5, 580 5. 6 10. 7

'5 8 It is seen from the above data that leather tanned using Test 2 the predominantly non-ionic, chromium-containing composition prepared in accordance with the method of the Abrasion Percent Water present invention by reacting lign-in sulfonic acid with be- Absorption Silicone, percent 0.10 M tween 25-50% sodium blchromate by weight of the hgrun 5 Inch sol-ids, is markedly more resistant to abrasion and water Hrs absorption than leather tanned with a chromium-containing tanning composition prepared by reacting only 26% g 353 g-g sodium bichrornate by weight of the lignin solids. This 0::II:I:II:IIIIIIIIIIII:I: 4617 13:0 27:3 clearly shows the superior properties of leather tanned in 10 it 2% accordance with the present invention. :I:I:I:III:IIIIIIIIIII: 61300 913 16.8

To further show the superiority of leather tanned in accordance with the present method, various commercially available vegetable-tanned sole leathers are subjected to From this data it is dearly Seen that the waterprooig the abrasion and Water absorption descnoed hererna-bove. 15 ness of the leathers prepared in accordance with the Pres Tm results of these tests are as follows: ent method is increased by treatment with a silicone resin and, additionally, that even where no silicone resin added to the leather, the abrasion and Water absorption Abrasion Percent water resistance is still greater than that of leather tanned using Leather 5 8 Absorption a chromium-containing tanning material prepared rei acting llgnm sulfonic acid with only 20% sodium bichromate by weight of the lignin solids.

K 9 258 1313 it? EXAMPLE 7 i 5Z6 55:6 To further demonstrate the advantage of leather tanned 575 8 9 in accordance with the present invention, a series of actual field tests of leather is carried out by resoling one shoe of each of three pairs and observing the actual wear obtained From these results it is clearly seen that leather tanned in 1186- Y this Procedure, thfi following data are in accordance with the present method has greatly suminedperior resistance to abrasion than commercially available vegetable tanned sole leather.

Moreover, it will be appreciated that leather tanned in Test Expert Control Hours Comments accordance with the present invention, i.e., in accordance Wear" mental S010 Worn with the method of Example 2, and retanned and fat liquored in accordance with the methods of Examples 3 1 Lem-m 360 ggg womr'Rcplm and 5, respectively, exhibits good resistance to Water ab- N11 1 2 Left Right 610 Control worn-Replace sorption. However, as set forth hereinabovc, increased 3Left Right 224 gfi W0m EXperi resistance to Water absorption can be obtained by submentnsmmd, jecting the thus-tanned leather to further treatment, such NO 2 Rightm 263 23E33 as with a silicone resin, e.g., Dow Corning Silicone 110 9. 2 Left Right.-- 945 Control WornExperi- To show the efiects of such further treatment, as well as mental Soundto substantiate the fact that the superior abrasion resist- I 40 ance obtalned oy leathers tanned in accordance with the present invention is not due to the addition of a silicone Control soles are good quality conventional vegetable resin, leathers produced in accordance with the method tanned leather soles, all control soles being at least as of Example 2 and then treated with varying amounts of thick as the experimental soles. All experimental soles the Dow Corning Silicone 1109, i.e., 045% by weight, were water-proofed with Dow Corning Silicone 1109. are subjected to the abrasion and water absorption test In carrying out the above tests, it is found that the exdescribed hereinabove. The results of these tests are as perimental soles give better traction on dry floors and follows: pavement. Tests were concluded when the uppers are completely Worn out, thus demonstrating that the sole Test 1 should last the life of the shoe under fairly hard service.

M an? EXAMPLE 8 Slhcone percent hill Further to illustrate the practice of the present invention with respect to the effect of vegetable retanning and 3 7 533 7 0 11' 4 chrome retanning of leather produced in accordance with 6:::::::::::::::::::::: 91 250 4.7 10.6 the present invention a senes of chemical analyses and 3 g: ig g strength tests were carried out and indexed comparatively a:IIIIIIIIIIIIIII: 6,383 10.5 in the following table, the data reported being based on G5 the weight of the tanned leather as is:

Percent Percent Percent Grease Percent Stitch Tensile Sample H2O CrzO Ash Hide SubpH Tear, Strength,

stance #Ilnfl #/h1.

A1 16.3 2.10 2.82 8.26 63.8 4.47 681 1855 A plus Tanoliu R Reta-n 17.5 4.18 4. 82 5.15 61. 6 3. 57 857 2138 A plus Vegetable Retan 15. 9 1.69 2. 23 6. 04 54. 9 3. 97 885 2910 1 Tanned with composition produced by reaction of 25% sodium bichromate with 100% lignin solids.

The above data demonstrates that it is possible further to improve the strength of the strong, firm leathers obtained in accordance with the practice of this invention by proper retanning.

EXAMPLE 9 To demonstrate the analysis involved in determining the form of chrome in various reaction products of sodium bichromate and lignin sulfonic acid, a sample is prepared using sodium bichromate in the amount of 25% by weight, based on the lignin sulfonic acid content. An aliquot of this sample, in the form of an aqueous solution, is then passed through a cation exchange column filled with chloride-free Dowex 50X1, and a difierent aliquot is passed through an anion exchange column, filled with sodium-free Dowex l-X1. The eflluent from each column is analyzed for chromium and the percentage of nonionic, anionic and cationic chromium calculated. The results of such test is set forth in the following table:

Percent Percent Percent Percent Sodium Anionic Cationic Non-Ionic Bichro- Chromium Chromium Chromium mate it is to be understood that although the invention has been described with specific reference to particular embodiments thereof, it is not to be so limited, since changes and alterations therein may be made which are within the hill intended scope of this invention as defined by the appended claims.

What is claimed is:

1. A leather tanning composition comprising the reaction product obtained by chemically reacting lignin sulfonic acid with a hexavalent chromium compound in an amount within the range of 25% to about 50% by weight of the lignin sulfonic acid, expressed as lignin solids, to produce a predominantly non-ionic chromiumcontaining material.

2. The tanning composition as claimed in claim 1 wherein the hexavalent chromium compound is an alkali metal bichromate.

3. The tanning composition as claimed in claim 2 wherein the alkali metal bichromate is sodium bichromate.

4. A tanning composition comprising the reaction product obtained by chemically reacting a major proportion of lignin sulfonic acid and a lesser amount of sodium bichromate sufiicient to produce a predominantly nonionie chromium-containing material, the amount of sodium bichromate being within the range of 25% to about 50% by weight of the lignin sulfonic acid expressed in terms of lignin solids.

5. The composition as claimed in claim 1 wherein the lignin sulfonic acid is produced in situ by acidification of an aqueous solution of water-soluble lignin solids.

6. The composition as claimed in claim wherein the acidification is accomplished by means of a mineral acid.

7. The composition as claimed in claim 1 wherein the reaction product is partially neutralized to a pH of about 4.0 to 5.0, inclusive.

8. A liquid tanning composition comprising the reaction product obtained by chemically reacting a solution of lignin sulfonic acid prepared by mineral acid acidification of an aqueous solution of water-soluble lignin solids with a solution of sodium bichromate, the sodium bi- Styrene type-sulionic acid cation exchange resin. Z Stznene typequaternary ammonium-chloride form anion exchange resin.

10 chromate being in an amount of at least 25% and not more than about 50% by weight, based on the lignin solids content.

9. The composition as claimed in claim 8 wherein the reaction product is partially neutralized to a pH of about 4.0 by addition of an alkali metal hydroxide.

10. The composition as claimed in claim 9 wherein the sodium bichromate is employed in an amount of 25% by weight of the lignin solids.

11. A process of producing a chromium tanning composition containing a major proportion of non-ionic chromium which comprises the steps of chemically reacting a major proportion of lignin sulfonic acid with a hexavalent chromium-containing compound in the amount within the range from 25% to about 50% by weight of the lignin sulfonic acid expressed in terms of lignin solids, to produce a predominantly non-ionic chromium-containing reaction product.

12. The method according to claim 11 wherein the reaction product is spray dried at an elevated temperature.

13. The method as claimed in claim 11 wherein the lignin sulfonic acid is produced in situ by acidification of a solution of dissolved lignin solids.

14. The method as claimed in claim 11 wherein the hexavalent chromium-containing compound is an alkali metal bichromate.

15. The method as claimed in claim 14 wherein the alkali metal bichromate is sodium bichromate.

16. A method of preparing a chromium tanning composition which comprises dissolving lignin solids in water, acidifying the resultant solution, slowly adding thereto with agitation, a solution of an alkali metal bichromate, the bichromate being in amount within the range of 25 to about 50% by weight of the lignin sulfonic acid expressed in terms of lignin solids, to produce a predominantly non-ionic chromium-containing material, the agitation being sufiicient to avoid lumping and continuing until the reaction is completed.

17. The method as claimed in claim 16 wherein the solution of lignin solids is acidified with a mineral acid.

18. The method as claimed in claim 17 wherein the reaction product is spray dried.

19. A method of preparing a chromium tanning composition which comprises dissolving lignin solids in water, adding thereto sulfuric acid in an amount of about 35% by weight of the lignin solids, agitating the thusformed mixture for about 1 hour, thereafter adding slowly a 50% by weight solution of sodium bichromate, with vigorous agitation, the amount of sodium bichromate added being within the range from 25% to 50% by weight of the lignin sulfonic acid expressed in terms of lignin solids, continuing agitation after all of the bichromate solution has been added for at least 2 hours, thereafter adding an alkali metal hydroxide solution with agitation so as to effect partial neutralization of the solution to a higher acid pH and subsequently adding a second portion of an alkali metal hydroxide to effect further neutralization to a still higher acid pH.

20. The method as claimed in claim 19 wherein the partially neutralized acid solution is spray dried.

References Cited in the file of this patent UNITED STATES PATENTS 1,316,742 Robeson Sept. 23, 1919 1,553,220 Cross Sept. 8, 1925 2,117,343 Merritt May 17, 1938 2,437,044 Robinson et al Mar. 2, 1948 2,766,098 Perrin Oct. 9, 1956 2,935,504 King et al. May 3, 1960 

4. A TANNING COMPOSITION COMPRISING THE REACTION PRODUCT OBTAINED BY CHEMICALLY REACTING A MAJOR PROPORTION OF LIGNIN SULFONIC ACID AND A LESSER AMOUNT OF SODIUM BICHROMATE SUFFICIENT TO PRODUCE A PREDOMINANTLY NONIONIC CHROMIUM-CONTAINING MATERIAL, THE AMOUNT OF SODIUM BICHROMATE BEING WITHIN THE RANGE OF 25% TO ABOUT 50% BY WEIGHT OF THE LIGNIN SULFONIC ACID EXPRESSED IN TERMS OF LIGNIN SOLIDS. 